The essays in this book highlight the most important ways in which domestic, international, public, and private legal systems interact with each other. The initial essays provide a theoretical overview of the study of legal harmonization—that is, of the nature and character of communication, accommodation, amalgamation, or resistance among legal systems. These interactions occur within horizontal relationships, between political institutions operating at the same level of authority. Vertical relationships between political institutions whose relationships are hierarchical have given rise to different patterns of interaction. New legal orders are being created through the adoption of international legal instruments that may reach nation-states, private entities, and individuals. Each has the potential for significantly affecting the sources of authority over public and private actors. Other essays illustrate the many ways in which communication between legal systems produce very real, if very different, effects across the world.